[X] My Assistant

[Floyd]

It has been quite cold in Boston for awhile, and as I sat in front a nice warm fire visiting Mars and Saturn at UMSF, my wife, Laura, asked whether fire is possible on planets without life. After some thought, I answered no.
I’m interested in your feedback. The things on Earth that burn ie wood, oil, coal, are mostly of organic origin. Furthermore, the oxygen in our atmosphere was put their largely by plants. Is the drastic chemical disequilibrium necessary for occasional surface fires on a planet dependent on living organisms? Are surface (forest) fires on a planet a sign of life? I’m sure this question has been addressed in science or literature (SF) before and would appreciate any references or links.

What other chemistries could produce a nice fire if we wanted a “bonfire” at Victoria for the UMSF picnic? Anything UMSFers could gather from the planet surface in a massive treasure hunt? I hope we don’t have to each bring a stick from Earth and an oxygen tank!
Floyd

[DEChengst]

We could mine sulfur at volcanoes, and nitrates from salt deposits. Mixing them up would make it burn pretty nice.

[dvandorn]

Well, yes, there are a number of different non-organic materials that will burn, given a decent percentage of oxygen in the air. Floyd's other point is still very valid, though -- the only mechanism I've ever heard of for achieving that decent percentage of oxygen in the air is via photosynthetic plants.

Now, if someone can give me a decent mechanism for getting a lot of free oxygen in the air without photosynthetic plants being present, then I'll agree that you can have open fires without life...

-the other Doug

[ugordan]

You don't necessarily need oxygen to burn stuff. Chlorine will do just fine as well.

[dvandorn]

Drat, I knew I should have added this in my first post:

"This is all assuming we're speaking of 'fire' in the familiar terms of rapid oxidation of flammable materials."

I think bringing chlorine into the discussion is rather like someone asking if there are waterfalls anywhere else in the solar system, since you need liquid water for them, and having someone point out the lakes, etc., on Titan. Yes, there is *fluid* in lakes on Titan, but ethane can't ever make a *water*fall...

-the other Doug

[nprev]

You want fire? Light a match on Titan, then open the airlock...

Not to go OT, but frankly I think that this facetious scenario will present an enormous obstacle for any future manned landings there...given one spark & any inward leakage of Titanian atmosphere, you got a probable kaboom... ...to say nothing of the potential flammability of some of the surface cryominerals if brought inside for analysis (or via suit contamination), even if kept cold.

[DEChengst]

"This is all assuming we're speaking of 'fire' in the familiar terms of rapid oxidation of flammable materials."

Having something like hydrogen react with chlorine would still be oxidation.

"Oxidation describes the loss of electrons by a molecule, atom or ion":

http://en.wikipedia.org/wiki/Redox

[Floyd]

Thanks for your responses.

I would define fire as a reaction that was fast and hot enough to give off visible light. Bringing sulfur and nitrates together would probably qualify, but needs someone to get distant materials and mix them together--added energy thermodynamically. So maybe another way to pose the problem is: Would lightning on any planet without life start a fire? Slow oxidation reactions most places would probably bring reactants to a near equilibrium?

Fire is something we take as so elemental in most world views: rock, air, water, fire. How amazing that in our solar system, we are the only planet currently with water lakes or fire. (Titan has beautiful, potentially flammable lakes, but fails my definitions—a liquid, but not not water, and we would have to bring the oxygen or another oxidizing gas to light it up the methane/ethane).

Has difficulty of making fire on lifeless planets ever shown up in science fiction works with which you are familiar?

[nprev]

Not that I recall, but I'd advise you to research the work of Hal Clement; he often wrote of radically different environments & biochemistries. If anybody ever tackled this topic, he's by far the most likely to have done so...good luck!

[deglr6328]

The question is important and cuts very deep to the most fundamental properties of life and nautre itself. We can rephrase the question more generally as "what are the limits of thermodynamic disequilibria in the atmospheres and surfaces of non-living planets?". I could imagine the ocassional very rare local flare up of say, sodium nitrate and sulfur or some such as DEChengst above suggests, but sustained burning of any kind.... I think you had the correct answer, no. The very method by which planets form, from very hot gas, dust, and rocks coalescing from a protoplanetary nebula, ensures that all oxidative reactions that CAN go WILL go in the first stages of a planets life. Since all atoms are free to break apart (and recombine later when things cool down), all molecular compounds on the new world should all be at pretty much their lowest energy state after emerging from such conditions. You need a source of negative entropy to start breaking those lowest energy state molecules into thier constituents to begin creating a thermodynamic disequilibrium. The sun of course, is an enourmous source of such energy but I can't see how simple irradiation with heat and light from a sun could create such disequilibrium. In the same way that for instance ozone, is created by and then just as soon destroyed by the sun's radiation, so should go any other highly reactive species created by simillar mechanism. There is no potential for "sequestration" and long term storage of the negative entropy from a star without the intermediary of life so far as I can see. What a fun thing to think about though. I'm by no means certain that I have the correct answer and I will surely be thinking about it some more when I'm lying in bed before I go to sleep tonight.

[helvick]

I'm a bit confused with the emphasis on making fire on a lifeless planet - a naked fire itself would be pointless exercise in any situation where there was no oxygen for a human (or other O2 based lifeform who might have an ancestral familiarity with fire) to breathe. An inability to support fire also prevents combustion engines which might be more of an issue.

Just to put this in perspective within our own planet's two major biochemical environments fire is only possible in one. Fire as a general principle is not possible under water (duh!) and we have plenty examples of theorized "life on watery bodies" examples both real and fictional (Europa is a stand out here, as for fiction the various TV series have done this to death - I can recall at least three which you can find easily at the end of a Google search, and it certainly has arisen as a backfill\side story in literary SF (Ken MacLeod, Engines of Light for example) and occassionally as a main theme (Solaris - Stanislaw Lem).

[alan]

Well, yes, there are a number of different non-organic materials that will burn, given a decent percentage of oxygen in the air. Floyd's other point is still very valid, though -- the only mechanism I've ever heard of for achieving that decent percentage of oxygen in the air is via photosynthetic plants.

Now, if someone can give me a decent mechanism for getting a lot of free oxygen in the air without photosynthetic plants being present, then I'll agree that you can have open fires without life...

-the other Doug

What if the atmosphere was made up of mostly water vapor. Ultraviolet light at the top of the atmosphere could break up the water molecules into hydrogen and oxygen. The hydrogen would be more likely to be lost from the atmoshere because of its lower molecular weight leaving behind the oxygen. Would this build up a significant amount of oxygen in the atmosphere?

[djellison]

Magnesium will happily burn in a CO2 atmosphere ( as anyone who's tried to put out Magnesium with a CO2 extinguisher will tell you )

Doug

[nprev]

Sounds like personal experience, Doug?

Sure enough, though: 2Mg + CO2--> 2MgO + C. Looks like this is a good candidate fuel for the next UMSF BBQ, but the hot dogs & marshmallows are probably gonna taste a little funky...

Not to wander too much, but this is apparently a VERY energetic reaction (the source I found said about 193 kCal); in fact, the proposed experiment was to burn magnesium in dry ice, which sounded horrendously dangerous for a lot of reasons. Makes me wonder if it might be worthwhile on Mars someday to refine magnesium from, say, the salts @ Gusev & use it as a fuel source...to say nothing of liberating carbon for other applications.

[tty]

I remember that somebody (Arthur C. Clarke?) once wrote a story where the recently proven existence of such high-temperature runaway oxidation on Earth was considered the clincher in proving that the planet was uninhabitable by Martian astronomers.

As for oxygen production by dissociation I don't think it could ever produce enough oxygen to sustain combustion. Large amounts of water in the atmosphere requires fairly high temperatures and also means violent weather (it's the water vapour that drives Earth's dramatic climate). This in turn means a lot of erosion and good opportunities for the loss of oxygen by oxidation.

[edstrick]

My understanding -- it may be wrong -- is that once you get it going, magnesium will happily burn in a nitrogen atmosphere. Supposedly, the white "ash" from burning magnesium in air is partly magnesium nitride.

[djellison]

I've never tried to put it out with a CO2 extinguisher - but I did demonstrate the (at a first level) unintuitive concept of CO2 puting out a burning splint but making burning Magnesium burn brighter to some younger students at school using a tank of the stuff a bell jar and an asbestos mat

Doug

[edstrick]

One thing I'm SURE of.... it won't burn in argon.

It MAY be Titanium that burns 21% oxide 79% nitride, not magnesium.

Factoids are those bits of information stuck in the folds of your grey-matter that just sort of fall out of the gaps when you bang on your head.

[Juramike]

Flourine will burn impressively well in a hydrogen atmosphere to produce HF.

This might be handy at a future barbeque on/in Jupiter. (No glass bottles please).

[helvick]

Apart from the already poisonous ambient atmosphere and 2.5g local gravity while floating in the Jovian cloud tops that HF exhaust definitely makes that one BBQ I'll have to pass on. The view might be pretty cool though.

[Stephen]

I remember that somebody (Arthur C. Clarke?) once wrote a story where the recently proven existence of such high-temperature runaway oxidation on Earth was considered the clincher in proving that the planet was uninhabitable by Martian astronomers.

Sounds like Clarke's tongue-in-cheek essay "Report on Planet Three" (which can be found in the 1972 collection "Report on Planet Three and Other Speculations").

======
Stephen

[nprev]

Good old Arthur C....how's he doing these days, anyhow? He wrote some of the most memorable & significant things in SF. It's a shame that we haven't seen anything new from him for awhile, but he is getting on in years...

Well, to redirect this discussion back to its original theme somewhat, I think that 'fire' is indeed probably a phenomenon restricted to worlds with an extensive biosphere. Although we only have one example to work with, life seems to be unique in the sense that it's generally anti-entropic, and actually causes a general energy imbalance in the local environment (i.e., free oxygen). This imbalance is of course crucial for maintaining living processes, but also can lead to runaway chemical reactions like fire.

What's interesting is that worlds that may harbor micro-environments favorable for life (like Mars) apparently do not exhibit a general entropic imbalance. Conversely, Europa is locked in a shell of ice and possibly may have a global habitable environment underneath, yet highly energetic reactions like fire just don't happen underwater. Perhaps the original question here should be constrained to considering only planets with extensive atmospheres...

[tty]

I agree - a high oxygen atmosphere is probably an excellent indication that there is life on a planet, and what is more, photosynthetic life or a reasonably close analogue. However the absence of oxygen does not prove the absence of an extensive biosphere. Our one example may have had an high-oxygen atmosphere for less than 25 % of the time life has existed here, and almost certainly for less than 50 %.

[nprev]

Excellent point, tty; anerobes rule!

Come to that, an oxygen-enriched atmosphere is really a very limited indicator, albeit an apparently unambiguous & quite detectable one. O2 allows high-energy organisms (and fires) to exist, but who's to say that a largely chemosynthetic rather than photosynthetic biosphere would not be equally viable or complex?

We know nothing yet, really...hope to live long enough to see some answers!

[JRehling]

[...]

[Juramike]

Another angle to this would be that you could potentially, on a lifeless planet, have a big fire (in O2, Fl2, or Cl2)... once. If some quirk of, let's say, the introduction of a hitherto trapped reservoir in the crust or in oceans made it's way to the atmosphere, you could get a single catastrophic burn-off that would last until the chemical energy were exhausted, and then end, forever.

Actually, you might get away with it more than once. The terrestrial analog would be a gas vent (petroleum, natural gas, methane in a swamp) lighting up in the oxygen atmosphere. It vents, it burns for a while, then burns itself out.

If there was a geochemical process that could regenerate the key reactive species (I haven't a clue how fluorine gas could be (oxidized?) back down to F2 geochemically), this whole process could repeat itself ad infinitum. All without having to invoke biology.

I would not be suprised to find that some very funky sulfur redox chemistry is occuring on Io right now, possibly involving generation of a flame somewhere in the cycle.